From the Jargon File (4.4.4, 14 Aug 2003):
A small, crocky feature that sticks out of an otherwise clean design. Something conspicuous for localized ugliness, especially a special-case exception to a general rule. For example, in some versions of csh(1), single quotes literalize every character inside them except !. In ANSI C, the ?? syntax used for obtaining ASCII characters in a foreign environment is a wart. See also miswart.Also, feel free to submit new warts. I will validate them then include them in this collection.